A gas turbine plant comprises at least a compressor, a combustion chamber and a turbine. In the compressor, aspirated air is compressed before a fuel is then added. This mixture is burned in the combustion chamber. The combustion exhaust gases are then fed to the turbine to generate power.
Gas turbine plants are nowadays equipped with multistage combustion chambers containing a plurality of burner stages to be operated in parallel with one another. These burner stages can be operated individually or jointly depending on the capacity utilization of the gas turbine plant. In addition to at least one main burner stage, the parallel burner stages comprise at least one pilot burner stage, the major part of the fuel being fed to the main burner stage.
Variations in the fuel flow supplied to the main and pilot burner stage result in output fluctuations and increased NOx emissions due to unstable combustion conditions. The output or more specifically the low NOx emissions are generally kept constant by controlling the fuel flow supplied to the main fuel stage and pilot fuel stage which are equipped with a size adjustable valve for this purpose. The fuel is generally present in gaseous form. In addition to solid particles already contained in the fuel, solid particles may be formed e.g. by sublimation of the fuel, particularly of sulfur contained in the fuel. These may be deposited inside the pipework.
However, deposits of solid particles in the fuel lines result in displacements of the valve characteristic and therefore in the fuel split, i.e. in the relative distribution of the fuel to the burner stages. In addition, there is a risk that less fuel is fed to individual stages or burners than is necessary for combustion. This results in increased emissions and combustion instabilities. In order to determine the extent of the deposits and, in the case of heavy deposits, to instigate cleaning action, the gas turbine plant has so far had to be shut down which is a very disadvantageous.